A compact S-band band-pass filter with ultra-wide stopband

Abstract

Abstract A novel compact S-band band-pass filter (BPF) with ultra-wide stopband is presented. The proposed filter mainly consists of three parts, a novel crossed resonator, parallel-coupled microstrip lines, and defect ground structures (DGSs). The resonator is constructed by three capacitive open stubs, while a defect is etched in the center stub to eliminate high frequency harmonics. The parallel-coupled microstrip lines are mainly used to improve the passband and the roll-off rate (the ratio of height to width of the filter transition band). And the DGSs are utilized to improve the stopband performances. The proposed BPF has the merits of compactness, good insertion loss and good stopband characteristic. The measured 3 dB operating band is 1.80–4.03 GHz (76.5% at f 0 = 2.92 GHz), The upper out-of-band suppression was better than 20 dB for the frequency up to 20 GHz (6.33f 0), and the upper roll-off rate reaches 75.59 dB/GHz.